Overexpression of the thymosin β-4 gene is associated with malignant progression of SW480 colon cancer cells

Abstract

Thymosin b-4 (Tb-4), a small peptide originally isolated from calf thymus, modulates the formation of F-actin microfilaments by sequestering the monomeric G-actin. Recent studies have shown that overexpression of the Tb-4 gene occurs not only in many human carcinomas but also in the highly metastatic melanomas and fibrosarcomas. However, little is known about the specific growth advantages acquired by different tumors from this genetic abnormality. To address the above questions, Tb-4-overexpressing human colon carcinoma (SW480) cells were established by stable transfection and their phenotypic changes were monitored. We found that both the morphology and the cortical actin cytoskeleton of SW480 cells were altered by Tb-4 overexpression. Moreover, both cellular level and that distributed over the intercellular junctions of the E-cadherin were decreased in the Tb-4 overexpressers, which were accompanied by a twofold increase in their saturation densities. Meanwhile, these cells also exhibited an increased ability to form colonies in soft agar. Interestingly, a dramatic increase of growth rate was detected in the Tb-4 overexpressers, which might be attributed to an accelerated proliferation induced by cMyc that was activated by nuclear b-catenin. Finally, a motility increase of these cells was demonstrated by two independent migration assays, which was accompanied by an enhanced focal contact. Taken together, our data suggest that the drastic growth property and motility changes of the SW480 cells overexpressing Tb-4 gene are due mainly to a deregulated cell-cell adhesion arisen from the downregulation of E-cadherin, plus uncontrolled cell proliferation owing to the upregulation of b-catenin, both resulted from a breakdown of actin microfilaments caused by the overexpression of this G-actin sequestering peptide.

Overexpression of the thymosin β-4 gene is associated with increased invasion of SW480 colon carcinoma cells and the distant metastasis of human colorectal carcinoma

“…In agreement with our in vitro observations (Wang et al, 2003), both the growth rate ( Figure 1a) and tumor weight (Figure 1b) of Tb-4 overexpressers (480S1 and 480S2) were significantly higher than those of the parental as well as the vectortransfected cells (480BK), demonstrating the importance of aberrant expression of this G-actin-sequestering protein in conferring in vivo growth advantages to colon cancer cells.…”

“…In fact, the invasion of cancer cells into nearby stroma, across blood vessel walls, and through normal epithelial cell layers have been shown to be promoted by various MMPs (Vihinen and Kahari, 2002). Since the levels of bcatenin, a well-known activator of MMP-7 (Brabletz et al, 1999), was found to be augmented in the Tb-4-overexpressing SW480 cells (Wang et al, 2003), increased MMP activities and a consequential enhanced invasion of these cells were postulated. Indeed, higher levels of MMP-7 were found in Tb-4 overexpressers ( Figure 2a) which were accompanied by a stronger protease activity (Figure 2b).…”

“…In a previous study, we have shown that disruption of the actin microfilaments in SW480 colon carcinoma cells by overexpressing a G-actin sequestering peptide, thymosin b-4 (Tb-4), results in a drastic change in cell growth and motility which is likely to be accounted by a deregulated cell-cell adhesion arisen from E-cadherin downregulation, plus an uncontrolled cell proliferation owing to an enhanced b-catenin signaling (Wang et al, 2003). Although these in vitro findings suggest an important role of Tb-4 upregulation in promoting the malignant progression of colon carcinoma cells, its in vivo effects are unclear.…”

Ku80 as a Novel Receptor for Thymosin β4 That Mediates Its Intracellular Activity Different from G-actin Sequestering

“…The increased expression of T␤4 correlates with the invasive capability of the cells, the degree of morphologic transformation, and disintegration of actin filaments (21). Recent studies have also correlated increased T␤4 expression with potentiated cell growth (13,22) but this observation seems not to be universal (2,10).…”

Thymosin 4 has tumor suppressive effects and its decreased expression results in poor prognosis and decreased survival in multiple myeloma

“…16,17 An adenoviralbased overexpression of Tβ4 was applied in a colon cancer and melanoma model showing increased growth, motility and invasive capacities in vitro and a larger tumor load in vivo. 18,19 Since proliferation, migration and invasion are part of the hallmarks of the biology of MM, we were interested in investigating an involvement of Tβ4 in this disease. We first investigated the Tβ4 expression pattern in 298 primary MM-cell samples and 14 normal plasma cell samples from healthy donors.…”